Large Extent of Convergent Evolution Towards the Double Histone Fold Revealed by Targeted Sequence and Structure Search Approach

Histone proteins are key players in chromatin packaging. In eukaryotes, nucleosomal cores—the DNA packaging fundamental units—are formed by composition of histone dimers. The double histone fold is a protein structure where two consecutive regions, each featuring histone fold, come together to create a histone pseudodimer. Although regarded as an uncommon fold to date, in this study we show—by protein structure and sequence analyses—that the double histone fold is widespread in eukaryotes. Perspectives of such outcome are discussed in terms of novel directions that our results may open in diverse areas, from epigenetics to the design of DNA-binding proteins.